The invention relates to a method for the application of liquid additives to the surface of continuous cylindrical products, for instance, a continuous filament rod such as is used in the manufacture of cigarette filters. Such fibrous rods are typically formed from a filamentary tow material comprising, e.g. cellulose esters such as cellulose acetate. Various methods are known for applying liquid additives such as plasticizers to the tow material to provide substantially uniform distribution of the additive throughout the tow, after which the material is compacted into a cylindrical rod, wrapped with paper known as plug wrap and, if desired, treated by the application of steam or hot air to accelerate "curing" or the action of the plasticizer on the tow material. Cigarette filter rod making machines are usually equipped with a center glue-line applicator. The center glue-line applicator is that part of the filter rod maker which applies glue to the paper that wraps the filter rod to bond the filter material to the wrapper.
One heretofore desired effect has been the relatively uniform interbonding among the fibers in the filter rod to form a relatively homogeneous structure of the desired density and resilience. For instance, Caines et al disclose in U.S. Pat. No. 3,099,594, FIG. 4, a circular air jet apparatus for the application and distribution of plasticizer to a bloomed or expanded bundle of tow, in which plasticizer can be introduced through the walls of the air jet in aerosol form. U.S. Pat. No. 3,157,536 (Caines) discloses an applicator having a cylindrical form wherein a plasticizer liquid flows into a cylindrical chamber, thereafter flowing outward through a slit in the side which is covered with screen and/or felt material. The system is used to coat a flattened tow ribbon which compacts the applicator near the slit in its outer wall and is thus coated with the plasticizer. A more commonly used applicator used in cigarette filter manufacturing is disclosed in U.S. Pat. No. 3,387,992.
Pryor discloses in U.S. Pat. No. 4,476,807 a method and apparatus for applying a uniform amount of an additive to a continuous, multifilament filter tow while the filter tow is in a loosely compacted substantially circular cross-sectional configuration. The additives are applied to the tow by strategically located nozzle means.
McArthur et al disclose in U.S. Pat. No. 3,560,298, FIG. 4, an air drying unit with an annular plenum surrounding a perforated tube through which a compacted filter rod passes. Air is introduced into the annular plenum through the outer wall. Roberts et al disclose in U.S. Pat. No. 3,852,009 a continuous porous belt which is wrapped around a mass of fiber to confine the fiber in a cylindrical rod configuration and convey it for processing, including passage through various plenum chambers in which fluids are introduced to heat or cool the rod product. Defensive Publication No. T892806 (Hollander) discloses apparatus for coating the outer surface of tubes or other containers with a liquid, wherein the tube passes through and in wiping contact with a resilient porous medium such as a sponge saturated with a liquid, the porous medium being retained in a combination holder and reservoir which is fed from a source of the coating liquid.
Although industrial processes for producing continuous cylindrical products such as fibrous rods suitable for the production of cigarette filters have been developed to a high degree, there is a continuing requirement for processes by which products meeting existing or higher standards can be produced, preferably with reduced consumption of energy and basic materials such as the tow and plasticizer used. Among the performance criteria considered in the evaluation of cigarette filters are filtration efficiency, pre-selected compressibility, plug wrap adherence and total weight.
Accordingly, it is an object of the present invention to provide an improved process for the application of liquid additives to a continuous cylindrical porous product. A more specific object is to provide an improved process for the peripheral application of a treating fluid such as a plasticizer to a continuous filament rod for the manufacture of cigarette filters. Another object is to provide a combined process for the combination of conventional homogeneous application of a treating fluid together with peripheral application of a treating fluid to a continuous filament rod. A further object of the invention is to provide a process for the application of a plasticizer to the surface of a continuous filament rod wherein a finished cigarette filter of desirable performance standards can be obtained while using a reduced amount of treating fluid per unit filter basis. A still further object of the invention is to provide a cigarette filter rod wrapped with plug wrap paper which is firmly adhered about the periphery of the filter rod without the application of a center-glue line.
Other objects and advantages of the present invention will be apparent to those skilled in the art from perusal of the following detailed description, the drawings and the appended claims.